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Overview of FRC Propulsion and Materials Research

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ISSUE: Plasma formation is the primary loss mechanism for ALL electrostatic or electromagnetic propulsion systems. It prevents operation at lower specific impulse, lowers efficiency at all exit velocities, and requires high mass propellants.

Solution: Entrain neutrals in an acceleration field after formation.

Benefit: Dramatic Increases in T/P across all specific impulses and propellants, including Air.

Thrust

Isp

Dynamic formation and acceleration of an FRC, shown with 4 field coils

What effects do high-temperature ion-wall interactions (even if they are very reduced) create if the ions are Oxygen, Nitrogen, or Hydrogen? In fusion plasmas the chemical sputtering rate can be more important than the purely kinetic energy sputtering rates.

Effects of magnetized plasma

FRC thrusters run with magnetically confined ions. This means pulsed, large magnetic fields (300-3000 Gauss), large gyroradii (possibly greater than the device), and very large electric fields at the wall (measured up to kV).

How does pulsed magnetic fields this change the wall interaction and lifetime picture?

Optical and Nuclear Radiation

A pulsed, high-temperature device will deliver pulsed optical radiation to the wall. This has effects for both contamination as well as the sputtering.

What are the effects of pulsed optical radiation on a thruster wall, both in terms of thermal loading and interaction with a neutral gas at the wall boundary.

FRC Propulsion Specific Interests

Magnetic Isolation dramatically limits plasma-wall interaction –

To what degree?

RMF – FRC Propulsion Materials Interests

Very long lifetimes must be demonstrated

ELF, EMPT development programs

Erosion of insulator. How small? Is an insulator needed?

RF coupling to high-temperature insulators (dissipation)

Quartz is great, but low thermal conductivity

BN, AlO, SiN FRC wall materials are unknown

Transient thermal and electromagnetic radiation loading is new for propulsion, must be studied

Demonstrated ionization and electromagnetic acceleration of a monopropellant

Fundamental Science

Task 2: Neutral Entrainment

ISSUE: Plasma formation is the primary loss mechanism for ALL electrostatic or electromagnetic propulsion systems. It prevents operation at lower specific impulse, lowers efficiency at all exit velocities, and requires high mass propellants.

Solution: Entrain neutrals in an acceleration field after formation.

Benefit: Specific impulse can be tailored to the mission, while the thruster operated at its maximum efficiency, even on light propellants.

Basic Idea: An FRC will ‘injest’ large quantities of neutral gas through charge exchange collisions, not ionization. If you accelerate an FRC while providing upstream neutral gas, Isp can be specified and mass/thrust added with very high efficiency [1].

High Power Helicon Thruster: Larger RF field amplitude at lower frequency leads to a much larger high density, high  plasma. Plasma is lost from stationary plasma through axial JBr as well as electro-thermal expansion. Detachment and beam spread problems greatly reduced.

Magnetically Accelerated Plasmoid Propulsion: With the FRC formed in ELF, further thrust or Isp can be obtained with peristaltic sequencing of axial array of flux coils. Large JBr force can be maintained throughout FRC passage enabling neutral gas entrainment significantly increasing thruster efficiency at optimal Isp.